In a meat packing plant, a conveyor is used for suspending an animal carcass in position to be trimmed and for moving the carcass from one station to another. Typically a carcass is attached to the conveyor on the kill floor and moved by the conveyor into a “hot box” where the carcass is cooled rapidly. The conveyor then takes the carcass to the sales cooler where the carcass is graded and either sold to a customer or processed. The moving parts of the conveyor from which the carcass has been detached then pass through an area where they are cleaned to remove soil and bacteria particularly from the parts that contact the carcass. These conveyor parts then move through a rinsing station and pass through a hot lubricant tank where lubricant is reapplied. When the moving parts of the conveyor exit the lubricant tank, they are blow-dried or sprayed with water so that excess lubricant is removed before they reenter the kill floor for attachment of a new carcass.
Conveyors for meat packing plants generally include gambrels, used for smaller carcasses, and trolleys, used for larger carcasses. In both cases, a rail is mounted along the path that the carcass is to take as it is processed. A wheel having an annular groove formed therein rolls on the rail. An axle pin extends through the wheel for supporting the gambrel or the trolley. Since the carcasses can weigh from 100 to 2300 pounds, there is a substantial load on the bearing surfaces of the pin and the wheel. These bearing surfaces must be lubricated so that the wheel will roll along the rail, making it easier for personnel or mechanical equipment to push the carcass along the path defined by the rail. If the lubricant is ineffective or becomes ineffective, it will be more difficult to move the carcass. In the worst case, the wheel does not rotate on the pin, such that the wheel becomes a “slider” that skids along the rail forming a “flat” on the surface of the wheel. This results in “down-time” to replace the wheel.
To avoid “sliders” the conveyor lubricant must function properly at the relatively warm and moist conditions existing in the kill room, where the carcass is first hung on the trolley; the cold and moist environment of the “hot box” where the temperature is maintained at or below 32° F. and the sales cooler where the temperature is at or slightly above 32° F. In the pork harvesting industry, the process bypasses the “hot box,” and instead goes through a blast freezer (aka, a “snap freezer”) for approximately 90 minutes at about −28° F. Thus, an important requirement for a lubricant used on a conveyor in a meat packing plant is that it be able to function both above and below the freezing temperature of water under a variety of conditions.
The lubricating properties of a lubricant are defined in terms of “lubricity” (i.e., the ability of the material to reduce friction and wear). In the practical sense of the term “lubricity” as applied to meat packing plant conveyors, the better the lubricity of a lubricant, the easier it is to push a given carcass along the conveyor, because a lubricant having good lubricity will enable the wheel to rotate relatively freely on the pin and to roll, not skid, along the rail. The lubricating properties of a lubricant are also defined by the “load bearing” capacity (aka, “wearability”), the ability of the lubricant to adhere and remain on the surface of the conveyor components.
A second key requirement for a lubricant used with a hook and trolley in a meat packing plant is that it be acceptable for use with products that are meant for human consumption. Because the conveyor is used in the processing of food for human consumption, the materials from which the lubricant is made and the resulting lubricant must comply with regulations of the U.S. Department of Agriculture (U.S.D.A.). Not all materials that have properties as a lubricant are sufficiently “non-toxic” to be safely used in food processing. For example, fluorinated hydrocarbons are frequently used in commercial lubricants and have very good lubricity and high temperature stability. However, they are not sufficiently “non-toxic” and, therefore, have not been approved by the U.S.D.A. for incidental contact with food. The U.S.D.A. regulations determine what materials may safely contact food products and, where appropriate, place limitations on the amount of such material which may safely remain on food products.
In particular, the Food and Drug Administration Regulations that govern the U.S.D.A.'s inspection service (21 CFR §178.3570) list certain materials which may be safely used on machinery for processing food where incidental contact with the food may occur. Among the materials generally listed as “lubricants” in that Section are certain fatty acids and oleates, certain mineral oils, and certain polybutenes and polyisobutylenes. However, mineral oil alone does not have sufficient lubricity to be acceptable as a carcass conveyor lubricant. Also, certain of the listed lubricants have limited permissible usage. For example, the polyisobutylenes are limited to use as a thickening agent in mineral oil lubricants.
21 CFR §178.3570 lists the following as lubricants for incidental contact with food as follows:                “Polybutene (minimum average molecular weight 80,000). Addition to food not to exceed 10 parts per million.        Polybutene, hydrogenated; complying with the identity prescribed under §178.3740.        Polyisobutylene (average molecular weight 35,000-140,000 [Flory]). For use only as a thickening agent in mineral oil lubricants.”        
Silicone compounds are registered as H1 lubricants that are approved for incidental food contact in food processing and food processing applications. In addition, silicone meets FDA 21 CFR 175.300 requirements for use as a lubricant for incidental contact with food. Silicone sprays are recommended to prevent plastic and foam from sticking in food processing and packaging areas. Suitable silicone compounds typically have a viscosity greater than about 300 centistokes.
The U.S.D.A. regulations list materials which may be used in food processing generally. There is no suggestion or recommendation on the U.S.D.A.'s approved list to use any of these materials specifically as a lubricant in a meat packing plant under the various conditions encountered there.
The classification of a material as being suitable for “incidental contact” with food means that the food contacted by the material should still be safely edible. Since the amount of the material which can be retained on the food and safely eaten may not exceed a defined number of parts per million established by the U.S.D.A., incidental contact of the material with the food should be minimized.
Incidental contact of lubricant with carcasses suspended from a conveyor in a meat packing plant occurs when the lubricant flows from the bearing surfaces of the pin and the wheel and from other surfaces of the gambrel or trolley under the force of gravity and drips onto the exposed surfaces of the carcass below. Part of the U.S.D.A.'s rigorous inspection of carcasses during processing is to detect lubricant that has dripped onto each carcass. By shining a bright light onto the carcass an inspector can locate areas contaminated by lubricant which reflect the light differently than the uncontaminated surfaces of the carcass. After the areas of lubricant contamination have been located on the carcass, the carcass is trimmed to remove the portions of meat containing lubricant. The carcass is then subject to re-inspection.
The necessity to trim, re-inspect and, if necessary, re-trim lubricant contaminated meat takes extra time, which increases the meat packer's costs. It also unnecessarily reduces the weight of the carcass, which lowers carcass yield and the meat packer's revenue.
The “dripping problem” results from the flow of lubricant from the conveyor surfaces, especially from the bearing surfaces of the pin and the wheel, after the carcass has been suspended from the conveyor. In addition, it is desirable to minimize lubricant dripping prior to carcass application, since the drip may land on other parts of the conveyor equipment which subsequently cause contamination of the meat. A lubricant that is relatively “drip-resistant” is one that drips a minimal amount from the conveyor surfaces under the temperature and load conditions that exist both before and after the carcass has been hung on the conveyor. A third requirement for an acceptable hook and trolley lubricant, therefore, is that it be sufficiently “drip-resistant” to minimize lubricant contact with the meat resulting in waste.
Attempts have been made to reduce the dripping problem. As early as 1975, attempts were made to use thinner (or less viscous) lubricants at the elevated temperatures (e.g., 175° F.) at which the lubricant is typically applied to the conveyor parts. The theory was that this would make it easier to remove excess lubricant from conveyor parts by the air blower or water spray. If most, if not all, of the excess lubricant were removed, then only a thin lubricant layer would remain on the conveyor parts minimizing the risk of lubricant subsequently dripping on the carcass after it was hung on the conveyor. However, experience indicated that the use of less viscous lubricants did not result in an adequate residual coating of lubricant on the moving conveyor parts and, therefore, did not provide sufficient lubricity on the conveyor for the carcass loads.
Other attempts to minimize the dripping problem while maintaining desired lubricity utilized substantially thicker (i.e., more viscous) lubricants with viscosities in excess of 200 centipoise (“cp”). The theory was that these lubricants would flow so slowly that they would not drip onto the carcasses. However, this very same property prevented enough excess lubricant from being removed by the air or water spray following the lubricating step. As a result, so much lubricant was retained on the gambrel and trolley components that the lubricant oozed and dripped excessively after loading of the carcass onto the conveyor. Although attempts were made, a way could not be found to apply successfully only a thin layer of these viscous materials.
Within the limitations imposed by compliance with the U.S.D.A. regulations, others have attempted using fatty acids to lubricate conveyors in meat packing plants. For example, castor oil or coco fatty acid have been used alone or in various mixtures with mineral oil. The fatty acids provide the lubricity lacking in the mineral oil, but increase the cost of the lubricant. Moreover, it has been noted that these mixtures do not have enough “drip-resistance” to minimize the dripping problem.
Others have tried mixing acetylated monoglycerides with mineral oil, which results in a lubricant having increased chemical stability and drip-resistance, but reduced lubricity.
In addition to the previously discussed requirements regarding lubricity, safety, and drip-resistance, there are other requirements for an acceptable lubricant useful in conveyors for meat packing plants. An acceptable lubricant should be rust resistant or rust inhibiting to avoid damage and deterioration of conveyor parts. Thus, the components of any lubricant mixture must also be compatible with an anti-rust additive, which itself must meet the safety requirements of the U.S.D.A.
In addition, the lubricant must be capable of being cleaned from the conveyor parts, which contact the carcass as these parts pass through each cleaning cycle on the conveyor. It is necessary to remove lubricant, dirt, and bacteria by steam, dissolution, or mechanical means to prevent the buildup of bacteria in the plant. On the other hand, the lubricant should not be so easily removable that lubricity is lost from load bearing or moving surfaces. It is difficult to reapply lubricant effectively to these important surfaces, if the lubricant were totally removed.
From the view of both plant operators and the lubricant manufacturer, the cost of the lubricant components should be as low as possible. In today's competitive meat industry, substantial amounts of money cannot be afforded for production costs. Indeed, the major impetus for use of a drip-resistant lubricant is to reduce costs. If this can be accomplished with a competitively priced lubricant, the cost savings for the meat packer are considerable.
Finally, to reduce manufacturing costs, the components of the lubricant should be relatively easy to handle. Heating, which may be required to change the physical properties of the lubricant material, should be minimized to reduce costs.
In summary, for many years there have been unsuccessful attempts to find lubricants that can optimize all the foregoing qualities: lubricity, safety, “drip-resistance,” rust resistance, economy of manufacture and use, and “cleanability.” Although, meat packers have switched lubricants often in an attempt to obtain a satisfactory lubricant, they continue to incur increased costs and lower revenues than possible with the improved lubricant of this invention.